Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg, Potsdam-Golm, Germany.
Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Straße, Haus, Potsdam-Golm, Germany.
J Exp Bot. 2022 Oct 18;73(18):6394-6404. doi: 10.1093/jxb/erac257.
Plants 'memorize' stressful events and protect themselves from future, often more severe, stresses. To maximize growth after stress, plants 'reset' or 'forget' memories of stressful situations, which requires an intricate balance between stress memory formation and the degree of forgetfulness. HEAT SHOCK PROTEIN 21 (HSP21) encodes a small heat shock protein in plastids of Arabidopsis thaliana. HSP21 functions as a key component of thermomemory, which requires a sustained elevated level of HSP21 during recovery from heat stress. A heat-induced metalloprotease, filamentation temperature-sensitive H6 (FtsH6), degrades HSP21 to its pre-stress abundance, thereby resetting memory during the recovery phase. The transcription factor heat shock factor A2 (HSFA2) activates downstream genes essential for mounting thermomemory, acting as a positive regulator in the process. Here, using a yeast one-hybrid screen, we identify HSFA2 as an upstream transactivator of the resetting element FtsH6. Constitutive and inducible overexpression of HSFA2 increases expression of FtsH6, whereas it is drastically reduced in the hsfa2 knockout mutant. Chromatin immunoprecipitation reveals in planta binding of HSFA2 to the FtsH6 promoter. Importantly, overexpression of HSFA2 improves thermomemory more profoundly in ftsh6 than wild-type plants. Thus, by activating both memory-supporting and memory-resetting genes, HSFA2 acts as a cellular homeostasis factor during thermomemory.
植物“记住”压力事件，并保护自己免受未来更严重的压力。为了在压力后最大限度地生长，植物会“重置”或“忘记”压力情况的记忆，这需要在压力记忆形成和遗忘程度之间进行复杂的平衡。热休克蛋白 21（HSP21）在拟南芥质体中编码一种小热休克蛋白。HSP21 作为热记忆的关键组成部分发挥作用，这需要在从热应激中恢复时持续升高 HSP21 水平。一种热诱导的金属蛋白酶，丝状温度敏感 H6（FtsH6），将 HSP21 降解为其应激前的丰度，从而在恢复阶段重置记忆。转录因子热休克因子 A2（HSFA2）激活下游对热记忆至关重要的基因，作为该过程中的正调节剂发挥作用。在这里，我们使用酵母单杂交筛选，鉴定 HSFA2 为重置元件 FtsH6 的上游反式激活因子。HSFA2 的组成型和诱导型过表达增加了 FtsH6 的表达，而在 hsfa2 敲除突变体中则大幅降低。染色质免疫沉淀揭示了 HSFA2 在体内与 FtsH6 启动子的结合。重要的是，与野生型植物相比，HSFA2 的过表达在 ftsh6 中更能改善热记忆。因此，HSFA2 通过激活支持记忆和重置记忆的基因，在热记忆过程中充当细胞内稳态因子。
